DNA binding by Ru(II)–bis(bipyridine)–pteridinyl complexes

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Abstract
The interactions of five bis(bipyridyl) Ru(II) complexes of pteridinyl-phenanthroline ligands with calf thymus DNA have been studied. The pteridinyl extensions were selected to provide hydrogen-bonding patterns complementary to the purine and pyrimidine bases of DNA and RNA. The study includes three new complexes [Ru(bpy)2(L-pterin)]2+, [Ru(bpy)2(L-amino)]2+, and [Ru(bpy)2(L-diamino)]2+ (bpy is 2,2′-bipyridine and L-pterin, L-amino, and L-diamino are phenanthroline fused to pterin, 4-aminopteridine, and 2,4-diaminopteridine), two previously reported complexes [Ru(bpy)2(L-allox)]2+ and [Ru(bpy)2(L-Me2allox)]2+ (L-allox and L-Me2allox are phenanthroline fused to alloxazine and 1,3-dimethyalloxazine), the well-known DNA intercalator [Ru(bpy)2(dppz)]2+ (dppz is dipyridophenazine), and the negative control [Ru(bpy)3]2+. Reported are the syntheses of the three new Ru–pteridinyl complexes and the results of calf thymus DNA binding experiments as probed by absorption and fluorescence spectroscopy, viscometry, and thermal denaturation titrations. All Ru–pteridine complexes bind to DNA via an intercalative mode of comparable strength. Two of these four complexes—[Ru(bpy)2(L-pterin)]2+ and [Ru(bpy)2(L-allox)]2+—exhibit biphasic DNA melting curves interpreted as reflecting exceptionally stable surface binding. Three new complexes—[Ru(bpy)2(L-diamino)]2+, [Ru(bpy)2(L-amino)]2 and [Ru(bpy)2(L-pterin)]2+—behave as DNA molecular “light switches.”

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